The present disclosure relates to a sheet decurling device and an ink-jet type image forming apparatus including this.
An ink-jet type image forming apparatus normally includes a sheet decurling device decurling a curled sheet. For instance, there is widely known a roller type sheet decurling device including a hard roller that comes into pressure contact with an elastic roller. However, the roller type sheet decurling device has a problem that it is difficult to assure a large (long) nip width, i.e., a distance in a sheet conveyance direction of the nip part.
Technologies solving the abovementioned problem are being proposed. For instance, a decurler (sheet decurling device) includes a belt wrapped around a plurality of rollers, instead of the elastic roller, and a hard roller. This belt type sheet decurling device can assure a large nip width because the belt is brought into pressure contact with the hard roller so as to be wrapped around the hard roller.
By the way, the decurler described above permits to change a decurling force applied on a sheet by increasing/decreasing an amount of the belt wrapped around the hard roller. However, if the amount of the belt wrapped around the hard roller decreases, a pressure applied by the hard roller to the belt also decreases. Then, because a sheet nipping force at the nip part drops, there is a case when the decurler is unable to adequately nip the sheet at the nip part. That is, there is a possibility of causing sheet conveyance failure, disabling to decurl the sheet. Meanwhile, if the amount of the belt wrapped around the hard roller increases, a pressure applied by the hard roller to the belt also increases. Therefore, there is a possibility of increasing a traveling load of the belt, while lowering a sheet conveyance speed.